Japanese Patent-Application Publication No. H8-101609 has proposed an image processing device including a main control unit and a sub-control unit. The main control unit controls each of various units, such as a printer unit, and the sub-control unit controls an interface for communicating with external devices. During a power-saving mode, the main control unit is placed in a halt state, and only the sub-control unit is in a running state. This configuration reduces power consumption in the power-saving mode.